Satellite radiotelephone systems, methods, components and devices including gated radiotelephone transmissions to ancillary terrestrial components

ABSTRACT

A satellite radiotelephone system includes a space-based component and an ancillary terrestrial component that are configured to receive wireless communications from radiotelephones. The radiotelephones are configured to transmit wireless communications to the ancillary terrestrial component over a range of satellite band forward link frequencies. The radiotelephone outputs are gated to cease transmissions periodically over a period of time. Related systems, methods, components and devices are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/147,048,filed Jun. 7, 2005, entitled Systems and Methods for Terrestrial Use ofCellular Satellite Frequency Spectrum, which is a continuation ofapplication Ser. No. 10/225,616, filed Aug. 22, 2002, entitledAdditional Systems and Methods for Monitoring Terrestrially ReusedSatellite Frequencies to Reduce Potential Interference, which itselfclaims the benefit of provisional Application No. 60/322,240, filed Sep.14, 2001, entitled Systems and Methods for Terrestrial Re-Use of MobileSatellite Spectrum, provisional Application No. 60/347,174, filed Jan.9, 2002, entitled Monitoring Terrestrially Reused Satellite Frequenciesto Reduce Potential Interference, and provisional Application No.60/392,754, filed Jul. 1, 2002, entitled Additional Systems and Methodsfor Monitoring Terrestrially Reused Satellite Frequencies to ReducePotential Interference. application Ser. No. 10/225,616 is acontinuation-in-part of application Ser. No. 10/074,097, filed Feb. 12,2002 (now U.S. Pat. No. 6,084,057), entitled Systems and Methods forTerrestrial Reuse of Cellular Satellite Frequency Spectrum and is also acontinuation-in-part of application Ser. No. 10/156,363, filed May 28,2002, entitled Systems and Methods for Monitoring Terrestrially ReusedSatellite Frequencies to Reduce Potential Interference. application Ser.No. 10/156,363 itself claims the benefit of provisional Application No.60/347,174, filed Jan. 9, 2002, entitled Monitoring Terrestrially ReusedSatellite Frequencies to Reduce Potential Interference; and itself is acontinuation-in-part of application Ser. No. 10/074,097, filed Feb. 12,2002 (now U.S. Pat. No. 6,684,057), entitled Systems and Methods forTerrestrial Reuse of Cellular Satellite Frequency Spectrum, which claimsthe benefit of provisional Application No. 60/322,240, filed Sep. 14,2001, entitled Systems and Methods for Terrestrial Re-Use of MobileSatellite Spectrum. All of these applications are assigned to theassignee of the present application, the disclosures of all of which arehereby incorporated herein by reference in their entirety as if setforth fully herein.

FIELD OF THE INVENTION

This invention relates to radiotelephone communications systems andmethods, and more particularly to terrestrial cellular and satellitecellular radiotelephone communications systems and methods.

BACKGROUND OF THE INVENTION

Satellite radiotelephone communications systems and methods are widelyused for radiotelephone communications. Satellite radiotelephonecommunications systems and methods generally employ at least onespace-based component, such as one or more satellites that areconfigured to wirelessly communicate with a plurality of satelliteradiotelephones.

A satellite radiotelephone communications system or method may utilize asingle antenna beam covering an entire area served by the system.Alternatively, in cellular satellite radiotelephone communicationssystems and methods, multiple beams are provided, each of which canserve distinct geographical areas in the overall service region, tocollectively serve an overall satellite footprint. Thus, a cellulararchitecture similar to that used in conventional terrestrial cellularradiotelephone systems and methods can be implemented in cellularsatellite-based systems and methods. The satellite typicallycommunicates with radiotelephones over a bidirectional communicationspathway, with radiotelephone communication signals being communicatedfrom the satellite to the radiotelephone over a downlink or forwardlink, and from the radiotelephone to the satellite over an uplink orreturn link.

The overall design and operation of cellular satellite radiotelephonesystems and methods are well known to those having skill in the art, andneed not be described further herein. Moreover, as used herein, the term“radiotelephone” includes cellular and/or satellite radiotelephones withor without a multi-line display; Personal Communications System (PCS)terminals that may combine a radiotelephone with data processing,facsimile and/or data communications capabilities; Personal DigitalAssistants (PDA) that can include a radio frequency transceiver and apager, Internet/intranet access, Web browser, organizer, calendar and/ora global positioning system (GPS) receiver; and/or conventional laptopand/or palmtop computers or other appliances, which include a radiofrequency transceiver.

As is well known to those having skill in the art, terrestrial networkscan enhance cellular satellite radiotelephone system availability,efficiency and/or economic viability by terrestrially reusing at leastsome of the frequency bands that are allocated to cellular satelliteradiotelephone systems. In particular, it is known that it may bedifficult for cellular satellite radiotelephone systems to reliablyserve densely populated areas, because the satellite signal may beblocked by high-rise structures and/or may not penetrate into buildings.As a result, the satellite spectrum may be underutilized or unutilizedin such areas. The use of terrestrial retransmission can reduce oreliminate this problem.

Moreover, the capacity of the overall system can be increasedsignificantly by the introduction of terrestrial retransmission, sinceterrestrial frequency reuse can be much denser than that of asatellite-only system. In fact, capacity can be enhanced where it may bemostly needed, i.e., densely populated urban/industrial/commercialareas. As a result, the overall system can become much more economicallyviable, as it may be able to serve a much larger subscriber base.Finally, satellite radiotelephones for a satellite radiotelephone systemhaving a terrestrial component within the same satellite frequency bandand using substantially the same air interface for both terrestrial andsatellite communications can be more cost effective and/or aestheticallyappealing. Conventional dual band/dual mode alternatives, such as thewell known Thuraya, Iridium and/or Globalstar dual modesatellite/terrestrial radiotelephone systems, may duplicate somecomponents, which may lead to increased cost, size and/or weight of theradiotelephone.

One example of terrestrial reuse of satellite frequencies is describedin U.S. Pat. No. 5,937,332 to the present inventor Karabinis entitledSatellite Telecommunications Repeaters and Retransmission Methods, thedisclosure of which is hereby incorporated herein by reference in itsentirety as if set forth fully herein. As described therein, satellitetelecommunications repeaters are provided which receive, amplify, andlocally retransmit the downlink signal received from a satellite therebyincreasing the effective downlink margin in the vicinity of thesatellite telecommunications repeaters and allowing an increase in thepenetration of uplink and downlink signals into buildings, foliage,transportation vehicles, and other objects which can reduce link margin.Both portable and non-portable repeaters are provided. See the abstractof U.S. Pat. No. 5,937,332.

In view of the above discussion, there continues to be a need forsystems and methods for terrestrial reuse of cellular satellitefrequencies that can allow improved reliability, capacity, costeffectiveness and/or aesthetic appeal for cellular satelliteradiotelephone systems, methods and/or satellite radiotelephones.

SUMMARY OF THE INVENTION

Some embodiments of the present invention provide systems and methodsfor terrestrial use of cellular satellite frequency spectrum. Morespecifically, according to some embodiments of the present invention, asatellite radiotelephone system comprises a space-based component thatis configured to receive wireless communications from radiotelephonesover a range of satellite band return link frequencies and to transmitwireless communications to radiotelephones over a range of satelliteband forward link frequencies. An ancillary terrestrial component isconfigured to receive wireless communications from radiotelephones overthe range of satellite band return link frequencies and to transmitwireless communications to radiotelephones over the range of satelliteband forward link frequencies.

In other embodiments of the present invention, the ancillary terrestrialcomponent is configured to transmit wireless communications toradiotelephones and to receive wireless communications fromradiotelephones over a range of satellite band return link frequencies.In still other embodiments of the invention, the ancillary terrestrialcomponent is configured to receive wireless communications fromradiotelephones over a range of satellite band return link frequenciesand to transmit wireless communications to radiotelephones over a rangeof satellite band forward link frequencies. In still other embodimentsof the present invention, the ancillary terrestrial component isconfigured to transmit wireless communications to radiotelephones and toreceive wireless communications from radiotelephones over a range ofsatellite band return link frequencies. In all of the above-describedembodiments, the radiotelephones may be located where a satellitefootprint of the space-based component and a cell of the ancillaryterrestrial component overlap.

It will be understood by those having skill in the art that embodimentsof the present invention have been described above primarily inconnection with satellite radiotelephone systems. However, otherembodiments of the present invention provide ancillary terrestrialcomponents for satellite radiotelephone systems, the radiotelephonesthemselves and analogous methods of operating a satellite radiotelephonesystem, an ancillary terrestrial network and/or a radiotelephone.

Finally, radiotelephones and operating methods according to otherembodiments of the present invention include an electronics system thatis configured to transmit wireless communications to the ancillaryterrestrial component over a range of satellite band forward linkfrequencies, wherein a radiotelephone output is gated to ceasetransmissions periodically over a period of time. The electronics systemmay be configured to transmit the wireless communications using a CodeDivision Multiple Access (CDMA) air interface. Analogous methods alsomay be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of cellular radiotelephone systems andmethods according to embodiments of the invention.

FIG. 2 is a block diagram of adaptive interference reducers according toembodiments of the present invention.

FIG. 3 is a spectrum diagram that illustrates satellite L-band frequencyallocations.

FIG. 4 is a schematic diagram of cellular satellite systems and methodsaccording to other embodiments of the present invention.

FIG. 5 illustrates time division duplex frame structures according toembodiments of the present invention.

FIG. 6 is a block diagram of architectures of ancillary terrestrialcomponents according to embodiments of the invention.

FIG. 7 is a block diagram of architectures of reconfigurableradiotelephones according to embodiments of the invention.

FIG. 8 graphically illustrates mapping of monotonically decreasing powerlevels to frequencies according to embodiments of the present invention.

FIG. 9 illustrates an ideal cell that is mapped to three power regionsand three associated carrier frequencies according to embodiments of theinvention.

FIG. 10 depicts a realistic cell that is mapped to three power regionsand three associated carrier frequencies according to embodiments of theinvention.

FIG. 11 illustrates two or more contiguous slots in a frame that areunoccupied according to embodiments of the present invention.

FIG. 12 illustrates loading of two or more contiguous slots with lowerpower transmissions according to embodiments of the present invention.

FIG. 13 is a flowchart of operations for monitoring according toembodiments of the present invention.

FIG. 14 is a flowchart of operations for monitoring signals on thesatellite radiotelephones return link according to embodiments of thepresent invention.

FIG. 15 is a block diagram of embodiments of monitoring frequencies fromother satellite cells that are reused terrestrially in a given cell,according to embodiments of the present invention.

FIG. 16 is a schematic diagram of cellular radiotelephone systems andmethods according to embodiments of the invention.

FIG. 17 graphically illustrates power spectral density of a GSM/GMSKcaller according to embodiments of the present invention.

FIG. 18 illustrates a seven-cell satellite frequency reuse pattern andterrestrial reuse of satellite uplink frequencies outside a givensatellite cell, according to some embodiments of the present invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention, however, should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. Like numbers refer to like elements throughout.

FIG. 1 is a schematic diagram of cellular satellite radiotelephonesystems and methods according to embodiments of the invention. As shownin FIG. 1, these cellular satellite radiotelephone systems and methods100 include at least one Space-Based Component (SBC) 110, such as asatellite. The space-based component 110 is configured to transmitwireless communications to a plurality of radiotelephones 120 a, 120 bin a satellite footprint comprising one or more satellite radiotelephonecells 130-130″″ over one or more satellite radiotelephone forward link(downlink) frequencies f_(D). The space-based component 110 isconfigured to receive wireless communications from, for example, a firstradiotelephone 120 a in the satellite radiotelephone cell 130 over asatellite radiotelephone return link (uplink) frequency f_(U). Anancillary terrestrial network, comprising at least one ancillaryterrestrial component 140, which may include an antenna 140 a and anelectronics system 140 b (for example, at least one antenna 140 a and atlast one electronics system 140 b), is configured to receive wirelesscommunications from, for example, a second radiotelephone 120 b in theradiotelephone cell 130 over the satellite radiotelephone uplinkfrequency, denoted f′_(U), which may be the same as f_(U). Thus, asillustrated in FIG. 1, radiotelephone 120 a may be communicating withthe space-based component 110 while radiotelephone 120 b may becommunicating with the ancillary terrestrial component 140. As shown inFIG. 1, the space-based component 110 also undesirably receives thewireless communications from the second radiotelephone 120 b in thesatellite radiotelephone cell 130 over the satellite radiotelephonefrequency f′_(U) as interference. More specifically, a potentialinterference path is shown at 150. In this potential interference path150, the return link signal of the second radiotelephone 120 b atcarrier frequency f′_(U) interferes with satellite communications. Thisinterference would generally be strongest when f=f_(U), because, in thatcase, the same return link frequency would be used for space-basedcomponent and ancillary terrestrial component communications over thesame satellite radiotelephone cell, and no spatial discriminationbetween satellite radiotelephone cells would appear to exist.

Still referring to FIG. 1, embodiments of satellite radiotelephonesystems/methods 100 can include at least one gateway 160 that caninclude an antenna 160 a and an electronics system 160 b that can beconnected to other networks 162 including terrestrial and/or otherradiotelephone networks. The gateway 160 also communicates with thespace-based component 110 over a satellite feeder link 112. The gateway160 also communicates with the ancillary terrestrial component 140,generally over a terrestrial link 142.

Still referring to FIG. 1, an Interference Reducer (IR) 170 a also maybe provided at least partially in the ancillary terrestrial componentelectronics system 140 b. Alternatively or additionally, an interferencereducer 170 b may be provided at least partially in the gatewayelectronics system 160 b. In yet other alternatives, the interferencereducer may be provided at least partially in other components of thecellular satellite system/method 100 instead of or in addition to theinterference reducer 170 a and/or 170 b. The interference reducer isresponsive to the space-based component 110 and to the ancillaryterrestrial component 140, and is configured to reduce the interferencefrom the wireless communications that are received by the space-basedcomponent 110 and is at least partially generated by the secondradiotelephone 120 b in the satellite radiotelephone cell 130 over thesatellite radiotelephone frequency f′_(U). The interference reducer 170a and/or 170 b uses the wireless communications f′_(U) that are intendedfor the ancillary terrestrial component 140 from the secondradiotelephone 120 b in the satellite radiotelephone cell 130 using thesatellite radiotelephone frequency f′_(U) to communicate with theancillary terrestrial component 140.

In embodiments of the invention, as shown in FIG. 1, the ancillaryterrestrial component 140 generally is closer to the first and secondradiotelephones 120 a and 120 b, respectively, than is the space-basedcomponent 110, such that the wireless communications from the secondradiotelephone 120 b are received by the ancillary terrestrial component140 prior to being received by the space-based component 110.

The interference reducer 170 a and/or 170 b is configured to generate aninterference cancellation signal comprising, for example, at least onedelayed replica of the wireless communications from the secondradiotelephone 120 b that are received by the ancillary terrestrialcomponent 140, and to subtract the delayed replica of the wirelesscommunications from the second radiotelephone 120 b that are received bythe ancillary terrestrial component 140 from the wireless communicationsthat are received from the space-based component 110. The interferencereduction signal may be transmitted from the ancillary terrestrialcomponent 140 to the gateway 160 over link 142 and/or using otherconventional techniques.

Thus, adaptive interference reduction techniques may be used to at leastpartially cancel the interfering signal, so that the same, or othernearby, satellite radiotelephone uplink frequency can be used in a givencell for communications by radiotelephones 120 with the satellite 110and with the ancillary terrestrial component 140. Accordingly, allfrequencies that are assigned to a given cell 130 may be used for bothradiotelephone 120 communications with the space-based component 110 andwith the ancillary terrestrial component 140. Conventional systems mayavoid terrestrial reuse of frequencies within a given satellite cellthat are being used within the satellite cell for satellitecommunications. Stated differently, conventionally, only frequenciesused by other satellite cells may be candidates for terrestrial reusewithin a given satellite cell. Beam-to-beam spatial isolation that isprovided by the satellite system was relied upon to reduce or minimizethe level of interference from the terrestrial operations into thesatellite operations. In sharp contrast, embodiments of the inventioncan use an interference reducer to allow all frequencies assigned to asatellite cell to be used terrestrially and for satellite radiotelephonecommunications.

Embodiments of the invention according to FIG. 1 may arise from arealization that the return link signal from the second radiotelephone120 b at u generally will be received and processed by the ancillaryterrestrial component 140 much earlier relative to the time when it willarrive at the satellite gateway 160 from the space-based component 110via the interference path 150. Accordingly, the interference signal atthe satellite gateway 160 b can be at least partially canceled. Thus, asshown in FIG. 1, an interference cancellation signal, such as thedemodulated ancillary terrestrial component signal, can be sent to thesatellite gateway 160 b by the interference reducer 170 a in theancillary terrestrial component 140, for example using link 142. In theinterference reducer 170 b at the gateway 160 b, a weighted (inamplitude and/or phase) replica of the signal may be formed using, forexample, adaptive transversal filter techniques that are well known tothose having skill in the art. Then, a transversal filter output signalis subtracted from the aggregate received satellite signal at frequencyf′_(U) that contains desired as well as interference signals. Thus, theinterference cancellation need not degrade the signal-to-noise ratio ofthe desired signal at the gateway 160, because a regenerated(noise-free) terrestrial signal, for example as regenerated by theancillary terrestrial component 140, can be used to perform interferencesuppression.

FIG. 2 is a block diagram of embodiments of adaptive interferencecancellers that may be located in the ancillary terrestrial component140, in the gateway 160, and/or in another component of the cellularradiotelephone system 100. As shown in FIG. 2, one or more controlalgorithms 204, known to those having skill in the art, may be used toadaptively adjust the coefficients of a plurality of transversal filters202 a-202 n. Adaptive algorithms, such as Least Mean Square Error(LMSE), Kalman, Fast Kalman, Zero Forcing and/or various combinationsthereof or other techniques may be used. It will be understood by thosehaving skill in the art that the architecture of FIG. 2 may be used withan LMSE algorithm. However, it also will be understood by those havingskill in the art that conventional architectural modifications may bemade to facilitate other control algorithms.

Additional embodiments of the invention now will be described withreference to FIG. 3, which illustrates L-band frequency allocationsincluding cellular radiotelephone system forward links and return links.As shown in FIG. 3, the space-to-ground L-band forward link (downlink)frequencies are assigned from 1525 Mhz to 1559 MHz. The ground-to-spaceL-band return link (uplink) frequencies occupy the band from 1626.5 MHzto 1660.5 MHz. Between the forward and return L-band links lie theGPS/GLONASS radionavigation band (from 1559 MHz to 1605 MHz).

In the detailed description to follow, GPS/GLONASS will be referred tosimply as GPS for the sake of brevity. Moreover, the acronyms ATC andSBC will be used for the ancillary terrestrial component and thespace-based component, respectively, for the sake of brevity.

As is known to those skilled in the art, GPS receivers may be extremelysensitive since they are designed to operate on very weakspread-spectrum radionavigation signals that arrive on the earth from aGPS satellite constellation. As a result, GPS receivers may to be highlysusceptible to in-band interference. ATCs that are configured to radiateL-band frequencies in the forward satellite band (1525 to 1559 MHz) canbe designed with very sharp out-of-band emissions filters to satisfy thestringent out-of-band spurious emissions desires of GPS.

Referring again to FIG. 1, some embodiments of the invention can providesystems and methods that can allow an ATC 140 to configure itself in oneof at least two modes. In accordance with a first mode, which may be astandard mode and may provide highest capacity, the ATC 140 transmits tothe radiotelephones 120 over the frequency range from 1525 MHz to 1559MHz, and receives transmissions from the radiotelephones 120 in thefrequency range from 1626.5 MHz to 1660.5 MHz, as illustrated in FIG. 3.In contrast, in a second mode of operation, the ATC 140 transmitswireless communications to the radiotelephones 120 over a modified rangeof satellite band forward link (downlink) frequencies. The modifiedrange of satellite band forward link frequencies may be selected toreduce, compared to the unmodified range of satellite band forward linkfrequencies, interference with wireless receivers such as GPS receiversthat operate outside the range of satellite band forward linkfrequencies.

Many modified ranges of satellite band forward link frequencies may beprovided according to embodiments of the present invention. In someembodiments, the modified range of satellite band forward linkfrequencies can be limited to a subset of the original range ofsatellite band forward link frequencies, so as to provide a guard bandof unused satellite band forward link frequencies. In other embodiments,all of the satellite band forward link frequencies are used, but thewireless communications to the radiotelephones are modified in a mannerto reduce interference with wireless receivers that operate outside therange of satellite band forward link frequencies. Combinations andsubcombinations of these and/or other techniques also may be used, aswill be described below.

It also will be understood that embodiments of the invention that willnow be described in connection with FIGS. 4-12 will be described interms of multiple mode ATCs 140 that can operate in a first standardmode using the standard forward and return links of FIG. 3, and in asecond or alternate mode that uses a modified range of satellite bandforward link frequencies and/or a modified range of satellite bandreturn link frequencies. These multiple mode ATCs can operate in thesecond, non-standard mode, as long as desirable, and can be switched tostandard mode otherwise. However, other embodiments of the presentinvention need not provide multiple mode ATCs but, rather, can provideATCs that operate using the modified range of satellite band forwardlink and/or return link frequencies.

Embodiments of the invention now will be described, wherein an ATCoperates with an SBC that is configured to receive wirelesscommunications from radiotelephones over a first range of satellite bandreturn link frequencies and to transmit wireless communications to theradiotelephones over a second range of satellite band forward linkfrequencies that is spaced apart from the first range. According tothese embodiments, the ATC is configured to use at least one timedivision duplex frequency to transmit wireless communications to theradiotelephones and to receive wireless communications from theradiotelephones at different times. In particular, in some embodiments,the at least one time division duplex frequency that is used to transmitwireless communications to the radiotelephones and to receive wirelesscommunications from the radiotelephones at different times, comprises aframe including a plurality of slots. At least a first one of the slotsis used to transmit wireless communications to the radiotelephones andat least a second one of the slots is used to receive wirelesscommunications from the radiotelephones. Thus, in some embodiments, theATC transmits and receives, in Time Division Duplex (TDD) mode, usingfrequencies from 1626.5 MHz to 1660.5 MHz. In some embodiments, all ATCsacross the entire network may have the statedconfiguration/reconfiguration flexibility. In other embodiments, onlysome ATCs may be reconfigurable.

FIG. 4 illustrates satellite systems and methods 400 according to someembodiments of the invention, including an ATC 140 communicating with aradiotelephone 120 b using a carrier frequency f″_(U) in TDD mode. FIG.5 illustrates an embodiment of a TDD frame structure. Assuming full-rateGSM (eight time slots per frame), up to four full-duplex voice circuitscan be supported by one TDD carrier. As shown in FIG. 5, the ATC 140transmits to the radiotelephone 120 b over, for example, time slotnumber 0. The radiotelephone 120 b receives and replies back to the ATC140 over, for example, time slot number 4. Time slots number 1 and 5 maybe used to establish communications with another radiotelephone, and soon.

A Broadcast Control CHannel (BCCH) is preferably transmitted from theATC 140 in standard mode, using a carrier frequency from below any guardband exclusion region. In other embodiments, a BCCH also can be definedusing a TDD carrier. In any of these embodiments, radiotelephones inidle mode can, per established GSM methodology, monitor the BCCH andreceive system-level and paging information. When a radiotelephone ispaged, the system decides what type of resource to allocate to theradiotelephone in order to establish the communications link. Whatevertype of resource is allocated for the radiotelephone communicationschannel (TDD mode or standard mode), the information is communicated tothe radiotelephone, for example as part of the call initializationroutine, and the radiotelephone configures itself appropriately.

It may be difficult for the TDD mode to co-exist with the standard modeover the same ATC, due, for example, to the ATC receiver LNA stage. Inparticular, assuming a mixture of standard and TDD mode GSM carriersover the same ATC, during the part of the frame when the TDD carriersare used to serve the forward link (when the ATC is transmitting TDD)enough energy may leak into the receiver front end of the same ATC todesensitize its LNA stage.

Techniques can be used to suppress the transmitted ATC energy over the1600 MHz portion of the band from desensitizing the ATC's receiver LNA,and thereby allow mixed standard mode and TDD frames. For example,isolation between outbound and inbound ATC front ends and/or antennasystem return loss may be increased or maximized. A switchableband-reject filter may be placed in front of the LNA stage. This filterwould be switched in the receiver chain (prior to the LNA) during thepart of the frame when the ATC is transmitting TDD, and switched outduring the rest of the time. An adaptive interference canceller can beconfigured at RF (prior to the LNA stage). If such techniques are used,suppression of the order of 70 dB can be attained, which may allow mixedstandard mode and TDD frames. However, the ATC complexity and/or costmay increase.

Thus, even though ATC LNA desensitization may be reduced or eliminated,it may use significant special engineering and attention and may not beeconomically worth the effort. Other embodiments, therefore, may keepTDD ATCs pure TDD, with the exception, perhaps, of the BCCH carrierwhich may not be used for traffic but only for broadcasting over thefirst part of the frame, consistent with TDD protocol. Moreover, RandomAccess CHannel (RACH) bursts may be timed so that they arrive at the ATCduring the second half of the TDD frame. In some embodiments, all TDDATCs may be equipped to enable reconfiguration in response to a command.

It is well recognized that during data communications or otherapplications, the forward link may use transmissions at higher ratesthan the return link. For example, in web browsing with aradiotelephone, mouse clicks and/or other user selections typically aretransmitted from the radiotelephone to the system. The system, however,in response to a user selection, may have to send large data files tothe radiotelephone. Hence, other embodiments of the invention may beconfigured to enable use of an increased or maximum number of time slotsper forward GSM carrier frame, to provide a higher downlink data rate tothe radiotelephones.

Thus, when a carrier frequency is configured to provide service in TDDmode, a decision may be made as to how many slots will be allocated toserving the forward link, and how many will be dedicated to the returnlink. Whatever the decision is, it may be desirable that it be adheredto by all TDD carriers used by the ATC, in order to reduce or avoid theLNA desensitization problem described earlier. In voice communications,the partition between forward and return link slots may be made in themiddle of the frame as voice activity typically is statisticallybidirectionally symmetrical. Hence, driven by voice, the center of theframe may be where the TDD partition is drawn.

To increase or maximize forward link throughput in data mode, data modeTDD carriers according to embodiments of the invention may use a morespectrally efficient modulation and/or protocol, such as the EDGEmodulation and/or protocol, on the forward link slots. The return linkslots may be based on a less spectrally efficient modulation and/orprotocol such as the GPRS (GMSK) modulation and/or protocol. The EDGEmodulation/protocol and the GPRS modulation/protocol are well known tothose having skill in the art, and need not be described further herein.Given an EDGE forward/GPRS return TDD carrier strategy, up to(384/2)=192 kbps may be supported on the forward link while on thereturn link the radiotelephone may transmit at up to (115/2)≈64 kbps.

In other embodiments, it also is possible to allocate six time slots ofan eight-slot frame for the forward link and only two for the returnlink. In these embodiments, for voice services, given the statisticallysymmetric nature of voice, the return link vocoder may need to becomparable with quarter-rate GSM, while the forward link vocoder canoperate at full-rate GSM, to yield six full-duplex voice circuits perGSM TDD-mode carrier (a voice capacity penalty of 25%). Subject to thisnon-symmetrical partitioning strategy, data rates of up to(384)(6/8)=288 kbps may be achieved on the forward link, with up to(115)(2/8)≈32 kbps on the return link.

FIG. 6 depicts an ATC architecture according to embodiments of theinvention, which can lend itself to automatic configuration between thetwo modes of standard GSM and TDD GSM on command, for example, from aNetwork Operations Center (NOC) via a Base Station Controller (BSC). Itwill be understood that in these embodiments, an antenna 620 cancorrespond to the antenna 140 a of FIGS. 1 and 4, and the remainder ofFIG. 6 can correspond to the electronics system 140 b of FIGS. 1 and 4.If a reconfiguration command for a particular carrier, or set ofcarriers, occurs while the carrier(s) are active and are supportingtraffic, then, via the in-band signaling Fast Associated Control CHannel(FACCH), all affected radiotelephones may be notified to alsoreconfigure themselves and/or switch over to new resources. Ifcarrier(s) are reconfigured from TDD mode to standard mode, automaticreassignment of the carrier(s) to the appropriate standard-mode ATCs,based, for example, on capacity demand and/or reuse pattern can beinitiated by the NOC. If, on the other hand, carrier(s) are reconfiguredfrom standard mode to TDD mode, automatic reassignment to theappropriate TDD-mode ATCs can take place on command from the NOC.

Still referring to FIG. 6, a switch 610 may remain closed when carriersare to be demodulated in the standard mode. In TDD mode, this switch 610may be open during the first half of the frame, when the ATC istransmitting, and closed during the second half of the frame, when theATC is receiving. Other embodiments also may be provided.

FIG. 6 assumes N transceivers per ATC sector, where N can be as small asone, since a minimum of one carrier per sector generally is desired.Each transceiver is assumed to operate over one GSM carrier pair (whenin standard mode) and can thus support up to eight full-duplex voicecircuits, neglecting BCCH channel overhead. Moreover, a standard GSMcarrier pair can support sixteen full-duplex voice circuits when inhalf-rate GSM mode, and up to thirty two full-duplex voice circuits whenin quarter-rate GSM mode.

When in TDD mode, the number of full duplex voice circuits may bereduced by a factor of two, assuming the same vocoder. However, in TDDmode, voice service can be offered via the half-rate GSM vocoder withalmost imperceptible quality degradation, in order to maintain invariantvoice capacity. FIG. 7 is a block diagram of a reconfigurableradiotelephone architecture that can communicate with a reconfigurableATC architecture of FIG. 6. In FIG. 7, an antenna 720 is provided, andthe remainder of FIG. 7 can provide embodiments of an electronics systemfor the radiotelephone.

It will be understood that the ability to reconfigure ATCs andradiotelephones according to embodiments of the invention may beobtained at a relatively small increase in cost. The cost may be mostlyin Non-Recurring Engineering (NRE) cost to develop software. Somerecurring cost may also be incurred, however, in that at least anadditional RF filter and a few electronically controlled switches may beused per ATC and radiotelephone. All other hardware/software can becommon to standard-mode and TDD-mode GSM.

Referring now to FIG. 8, other radiotelephone systems and methodsaccording to embodiments of the invention now will be described. Inthese embodiments, the modified second range of satellite band forwardlink frequencies includes a plurality of frequencies in the second rangeof satellite band forward link frequencies that are transmitted by theATCs to the radiotelephones at a power level, such as maximum powerlevel, that monotonically decreases as a function of (increasing)frequency. More specifically, as will be described below, in someembodiments, the modified second range of satellite band forward linkfrequencies includes a subset of frequencies proximate to a first orsecond end of the range of satellite band forward link frequencies thatare transmitted by the ATC to the radiotelephones at a power level, suchas a maximum power level, that monotonically decreases toward the firstor second end of the second range of satellite band forward linkfrequencies. In still other embodiments, the first range of satelliteband return link frequencies is contained in an L-band of satellitefrequencies above GPS frequencies and the second range of satellite bandforward link frequencies is contained in the L-band of satellitefrequencies below the GPS frequencies. The modified second range ofsatellite band forward link frequencies includes a subset of frequenciesproximate to an end of the second range of satellite band forward linkfrequencies adjacent the GPS frequencies that are transmitted by the ATCto the radiotelephones at a power level, such as a maximum power level,that monotonically decreases toward the end of the second range ofsatellite band forward link frequencies adjacent the GPS frequencies.

Without being bound by any theory of operation, a theoretical discussionof the mapping of ATC maximum power levels to carrier frequenciesaccording to embodiments of the present invention now will be described.Referring to FIG. 8, let ν=

(ρ) represent a mapping from the power (ρ) domain to the frequency (ν)range. The power (ρ) is the power that an ATC uses or should transmit inorder to reliably communicate with a given radiotelephone. This powermay depend on many factors such as the radiotelephone's distance fromthe ATC, the blockage between the radiotelephone and the ATC, the levelof multipath fading in the channel, etc., and as a result, will, ingeneral, change as a function of time. Hence, the power used generallyis determined adaptively (iteratively) via closed-loop power control,between the radiotelephone and ATC.

The frequency (ν) is the satellite carrier frequency that the ATC usesto communicate with the radiotelephone. According to embodiments of theinvention, the mapping

is a monotonically decreasing function of the independent variable ρ.Consequently, in some embodiments, as the maximum ATC power increases,the carrier frequency that the ATC uses to establish and/or maintain thecommunications link decreases. FIG. 8 illustrates an embodiment of apiece-wise continuous monotonically decreasing (stair-case) function.Other monotonic functions may be used, including linear and/ornonlinear, constant and/or variable decreases. FACCH or Slow AssociatedControl CHannel (SACCH) messaging may be used in embodiments of theinvention to facilitate the mapping adaptively and in substantially realtime.

FIG. 9 depicts an ideal cell according to embodiments of the invention,where, for illustration purposes, three power regions and threeassociated carrier frequencies (or carrier frequency sets) are beingused to partition a cell. For simplicity, one ATC transmitter at thecenter of the idealized cell is assumed with no sectorization. Inembodiments of FIG. 9, the frequency (or frequency set) f_(I) is takenfrom substantially the upper-most portion of the L-band forward linkfrequency set, for example from substantially close to 1559 MHz (seeFIG. 3). Correspondingly, the frequency (or frequency set) f_(M) istaken from substantially the central portion of the L-band forward linkfrequency set (see FIG. 3). In concert with the above, the frequency (orfrequency set) f_(O) is taken from substantially the lowest portion ofthe L-band forward link frequencies, for example close to 1525 MHz (seeFIG. 3).

Thus, according to embodiments of FIG. 9, if a radiotelephone is beingserved within the outer-most ring of the cell, that radiotelephone isbeing served via frequency f_(O). This radiotelephone, being within thefurthest area from the ATC, has (presumably) requested maximum (or nearmaximum) power output from the ATC. In response to the maximum (or nearmaximum) output power request, the ATC uses its a priori knowledge ofpower-to-frequency mapping, such as a three-step staircase function ofFIG. 9. Thus, the ATC serves the radiotelephone with a low-valuefrequency taken from the lowest portion of the mobile L-band forwardlink frequency set, for example, from as close to 1525 MHz as possible.This, then, can provide additional safeguard to any GPS receiver unitthat may be in the vicinity of the ATC.

Embodiments of FIG. 9 may be regarded as idealized because theyassociate concentric ring areas with carrier frequencies (or carrierfrequency sets) used by an ATC to serve its area. In reality, concentricring areas generally will not be the case. For example, a radiotelephonecan be close to the ATC that is serving it, but with significantblockage between the radiotelephone and the ATC due to a building. Thisradiotelephone, even though relatively close to the ATC, may alsorequest maximum (or near maximum) output power from the ATC. With thisin mind, FIG. 10 may depict a more realistic set of area contours thatmay be associated with the frequencies being used by the ATC to serveits territory, according to embodiments of the invention. The frequency(or frequency set) f, may be reused in the immediately adjacent ATCcells owing to the limited geographical span associated with f, relativeto the distance between cell centers. This may also hold for f_(M).

Referring now to FIG. 11, other modified second ranges of satellite bandforward link frequencies that can be used by ATCs according toembodiments of the present invention now will be described. In theseembodiments, at least one frequency in the modified second range ofsatellite band forward link frequencies that is transmitted by the ATCto the radiotelephones comprises a frame including a plurality of slots.In these embodiments, at least two contiguous slots in the frame that istransmitted by the ATC to the radiotelephones are left unoccupied. Inother embodiments, three contiguous slots in the frame that istransmitted by the ATC to the radiotelephones are left unoccupied. Inyet other embodiments, at least two contiguous slots in the frame thatis transmitted by the ATC to the radiotelephones are transmitted atlower power than remaining slots in the frame. In still otherembodiments, three contiguous slots in the frame that is transmitted bythe ATC to the radiotelephones are transmitted at lower power thanremaining slots in the frame. In yet other embodiments, the lower powerslots may be used with first selected ones of the radiotelephones thatare relatively close to the ATC and/or are experiencing relatively smallsignal blockage, and the remaining slots are transmitted at higher powerto second selected ones of the radiotelephones that are relatively farfrom the ATC and/or are experiencing relatively high signal blockage.

Stated differently, in accordance with some embodiments of theinvention, only a portion of the TDMA frame is utilized. For example,only the first four (or last four, or any contiguous four) time slots ofa full-rate GSM frame are used to support traffic. The remaining slotsare left unoccupied (empty). In these embodiments, capacity may be lost.However, as has been described previously, for voice services, half-rateand even quarter-rate GSM may be invoked to gain capacity back, withsome potential degradation in voice quality. The slots that are notutilized preferably are contiguous, such as slots 0 through 3 or 4through 7 (or 2 through 5, etc.). The use of non-contiguous slots suchas 0, 2, 4, and 6, for example, may be less desirable. FIG. 11illustrates four slots (4-7) being used and four contiguous slots (0-3)being empty in a GSM frame.

It has been found experimentally, according to these embodiments of theinvention, that GPS receivers can perform significantly better when theinterval between interference bursts is increased or maximized. Withoutbeing bound by any theory of operation, this effect may be due to therelationship between the code repetition period of the GPS C/A code (1msec.) and the GSM burst duration (about 0.577 msec.). With a GSM frameoccupancy comprising alternate slots, each GPS signal code period canexperience at least one “hit”, whereas a GSM frame occupancy comprisingfour to five contiguous slots allows the GPS receiver to derivesufficient clean information so as to “flywheel” through the errorevents.

According to other embodiments of the invention, embodiments of FIGS.8-10 can be combined with embodiments of FIG. 11. Furthermore, accordingto other embodiments of the invention, if an f_(I) carrier of FIG. 9 or10 is underutilized, because of the relatively small footprint of theinner-most region of the cell, it may be used to support additionaltraffic over the much larger outermost region of the cell.

Thus, for example, assume that only the first four slots in each frameof f_(I) are being used for inner region traffic. In embodiments ofFIGS. 8-10, these four f_(I) slots are carrying relatively low powerbursts, for example of the order of 100 mW or less, and may, therefore,appear as (almost) unoccupied from an interference point of view.Loading the remaining four (contiguous) time slots of f_(I) withrelatively high-power bursts may have negligible effect on a GPSreceiver because the GPS receiver would continue to operate reliablybased on the benign contiguous time interval occupied by the fourlow-power GSM bursts. FIG. 12 illustrates embodiments of a frame atcarrier f_(I) supporting four low-power (inner interval) users and fourhigh-power (outer interval) users. In fact, embodiments illustrated inFIG. 12 may be a preferred strategy for the set of available carrierfrequencies that are closest to the GPS band. These embodiments mayavoid undue capacity loss by more fully loading the carrier frequencies.

The experimental finding that interference from GSM carriers can berelatively benign to GPS receivers provided that no more than, forexample, 5 slots per 8 slot GSM frame are used in a contiguous fashioncan be very useful. It can be particularly useful since thisexperimental finding may hold even when the GSM carrier frequency isbrought very close to the GPS band (as close as 1558.5 MHz) and thepower level is set relatively high. For example, with five contiguoustime slots per frame populated, the worst-case measured GPS receiver mayattain at least 30 dB of desensitization margin, over the entire ATCservice area, even when the ATC is radiating at 1558.5 MHz. With fourcontiguous time slots per frame populated, an additional 10 dBdesensitization margin may be gained for a total of 40 dB for theworst-case measured GPS receiver, even when the ATC is radiating at1558.5 MHz.

There still may be concern about the potential loss in network capacity(especially in data mode) that may be incurred over the frequencyinterval where embodiments of FIG. 11 are used to underpopulate theframe. Moreover, even though embodiments of FIG. 12 can avoid capacityloss by fully loading the carrier, they may do so subject to theconstraint of filling up the frame with both low-power and high-powerusers. Moreover, if forward link carriers are limited to 5 contiguoushigh power slots per frame, the maximum forward link data rate percaller that may be aimed at a particular user, may becomeproportionately less.

Therefore, in other embodiments, carriers which are subject tocontiguous empty/low power slots are not used for the forward link.Instead, they are used for the return link. Consequently, in someembodiments, at least part of the ATC is configured in reverse frequencymode compared to the SBC in order to allow maximum data rates over theforward link throughout the entire network. On the reverse frequencyreturn link, a radiotelephone may be limited to a maximum of 5 slots perframe, which can be adequate for the return link. Whether the fiveavailable time slots per frame, on a reverse frequency return linkcarrier, are assigned to one radiotelephone or to five differentradiotelephones, they can be assigned contiguously in these embodiments.As was described in connection with FIG. 12, these five contiguous slotscan be assigned to high-power users while the remaining three slots maybe used to serve low-power users.

Other embodiments may be based on operating the ATC entirely in reversefrequency mode compared to the SBC. In these embodiments, an ATCtransmits over the satellite return link frequencies whileradiotelephones respond over the satellite forward link frequencies. Ifsufficient contiguous spectrum exists to support CDMA technologies, andin particular the emerging Wideband-CDMA 3G standard, the ATC forwardlink can be based on Wideband-CDMA to increase or maximize datathroughput capabilities. Interference with GPS may not be an issue sincethe ATCs transmit over the satellite return link in these embodiments.Instead, interference may become a concern for the radiotelephones.Based, however, on embodiments of FIGS. 11-12, the radiotelephones canbe configured to transmit GSM since ATC return link rates are expected,in any event, to be lower than those of the forward link. Accordingly,the ATC return link may employ GPRS-based data modes, possibly evenEDGE. Thus, return link carriers that fall within a predeterminedfrequency interval from the GPS band-edge of 1559 MHz, can be underloaded, per embodiments of FIG. 11 or 12, to satisfy GPS interferenceconcerns.

Finally, other embodiments may use a partial or total reverse frequencymode and may use CDMA on both forward and return links. In theseembodiments, the ATC forward link to the radiotelephones utilizes thefrequencies of the satellite return link (1626.5 MHz to 1660.5 MHz)whereas the ATC return link from the radiotelephones uses thefrequencies of the satellite forward link (1525 MHz to 1559 MHz). TheATC forward link can be based on an existing or developing CDMAtechnology (e.g., IS-95, Wideband-CDMA, etc.). The ATC network returnlink can also be based on an existing or developing CDMA technologyprovided that the radiotelephone's output is gated to ceasetransmissions for approximately 3 msec once every T msec. In someembodiments, T will be greater than or equal to 6 msec.

This gating may not be needed for ATC return link carriers atapproximately 1550 MHz or below. This gating can reduce or minimizeout-of-band interference (desensitization) effects for GPS receivers inthe vicinity of an ATC. To increase the benefit to GPS, the gatingbetween all radiotelephones over an entire ATC service area can besubstantially synchronized. Additional benefit to GPS may be derivedfrom system-wide synchronization of gating. The ATCs can instruct allactive radiotelephones regarding the gating epoch. All ATCs can bemutually synchronized via GPS.

Monitoring Terrestrially Reused Satellite Frequencies to ReducePotential Interference

As was described above, for example, in connection with FIGS. 1 and 2,an ancillary terrestrial network comprising one or more ancillaryterrestrial components 140 in each satellite radiotelephone cell 130,may be used to enhance the cellular satellite radiotelephone systemavailability, efficiency and/or economic viability, by terrestriallyreusing at least some of the frequency bands that are allocated tocellular satellite radiotelephone systems. Thus, as was described, forexample, in connection with FIG. 1, in a given satellite cell 130 thatuses one or more frequencies within the satellite radiotelephonefrequency band for satellite communications, the frequencies ofsatellite cell 130, and at least some frequencies of the remainingsatellite cells 130′-130″″ also may be reused terrestrially by theancillary terrestrial network within the given satellite cell 130.Moreover, as was also described in connection with FIG. 1, the one ormore satellite uplink frequencies that are used in the given cell mayalso be reused terrestrially, using interference reducing techniques.Thus, within a given satellite cell, terrestrial reuse of some or all ofthe satellite frequencies may occur.

Unfortunately, the signals that are radiated by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith, may be sufficiently strong and/or numerous to potentiallyinterfere with other satellite radiotelephone systems, even when they donot interfere with satellite radiotelephone systems according toembodiments of the present invention.

In order to reduce or eliminate interference by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith, with other satellite radiotelephone systems, some embodimentsof the present invention can include systems and methods for monitoringterrestrially reused satellite frequencies and can control the number,geographic distribution and/or power of the radiation by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith, to reduce or eliminate potential interference with othersatellite radiotelephone systems. Interference within the givensatellite radiotelephone system (intra-system interference) also may bereduced by this monitoring, according to some embodiments of the presentinvention.

Thus, as shown in FIG. 16, satellite radiotelephone systems and methodsaccording to some embodiments of the invention include a space-basedcomponent 1630 (also referred to as a first space-based component) andan ancillary terrestrial network 1610, that are marketed, for example,by Mobile Satellite Ventures LP (“MSV”), the assignee of the presentapplication. The ancillary terrestrial network 1610 and/or theradiotelephones that communicate therewith (also referred to as aplurality of first radiotelephones), can radiate uplink signals 1620that may be sufficiently strong to be captured by the space-basedcomponent 1630 of the cellular satellite radiotelephone system. Thesesignals from the ancillary terrestrial network 1610 also may act asinterfering signals 1640 for a satellite 1650 (also referred to as asecond space-based component) of another satellite radiotelephonesystem, such as the Inmarsat system. According to some embodiments ofthe present invention, systems and methods may be provided formonitoring terrestrially reused satellite frequencies, for example byproviding a monitoring signal 1660 to a gateway 1670 of the satelliteradiotelephone system. The number, geographic distribution and/or powerof the radiation by the ancillary terrestrial network 1610 and/or theradiotelephones that communicate therewith may be controlled by acontroller 1680, to reduce or eliminate the interference 1640 with thesecond space-based component 1650. In other embodiments, the number,geographic distribution and/or power of the radiation by radiotelephonesthat communicate directly with the space-based component 1630 (alsoreferred to as a plurality of second radiotelephones) also may bemonitored and/or controlled. It will be understood by those having skillin the art that at last some of the plurality of first radiotelephonesalso may be configured to communicate directly with the secondspace-based component 1650 and that at least some of the plurality ofsecond radiotelephones also may be configured to communicate directlywith the first space-based component 1630, such that at least some ofthe plurality of first and second radiotelephones are capable ofchanging roles or playing both roles.

FIG. 13 is a flowchart illustrating overall operations for monitoringradiation generated by an ancillary terrestrial network and/or theradiotelephones that communicate therewith, and adjusting the radiationby the ancillary terrestrial network and/or the radiotelephone thatcommunicate therewith in response to the monitoring, according toembodiments of the present invention. These operations may be performed,for example, by the space-based component 1630, gateway 1670 and/orcontroller 1680 of FIG. 16.

Referring to FIG. 13, at Block 1310, the signals on the satelliteradiotelephone return link (uplink), for example link 1620 of FIG. 16,are monitored to identify signals that are generated by the ancillaryterrestrial network, such as the ancillary terrestrial network 1610 ofFIG. 16, and/or the radiotelephones that communicate therewith. At Block1320, if the signals are excessive, so as to potentially interfere withother satellite radiotelephone systems, such as the satellite 1650 ofFIG. 16, then, at Block 1330, the radiation by the ancillary terrestrialnetwork and/or the radiotelephones that communicate therewith can bereduced selectively. Alternatively, if the signals are not excessive atBlock 1320, then the radiation by the ancillary terrestrial networkand/or the radiotelephones that communicate therewith can remain at thesame level or can be increased at Block 1340. Monitoring according tosome embodiments of the invention may be provided repeatedly, on acontinuous basis, or periodically.

Referring now to FIG. 14, additional details of monitoring (Block 1310of FIG. 13) according to some embodiments of the invention now will bedescribed. In particular, at Block 1310, the signals on the satelliteradiotelephone return link are monitored to detect radiation by theancillary terrestrial network and/or the radiotelephones thatcommunicate therewith. Two types of radiation by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith in a given satellite cell may be monitored. In firstembodiments of monitoring, the monitored radiation includes radiation,by the ancillary terrestrial network and/or radiotelephones that cancommunicate therewith in a given satellite cell, of frequencies that arenot used for space-based communications within the given satelliteradiotelephone cell (Block 1410). In second embodiments of monitoring,the monitored radiation includes radiation, by the ancillary terrestrialnetwork and/or radiotelephones that communicate therewith in a givensatellite cell, of satellite frequencies that are used by thespace-based component within the given satellite cell and also arereused by the ancillary terrestrial network in the given cell (Block1420). Each of these embodiments of monitoring will now be described indetail.

In the first embodiments of monitoring (Block 1410), a frequency or setof frequencies is used for space-based communications within a givensatellite cell. Satellite frequencies other than this set of frequenciesmay be used by other satellite cells and also may be reusedterrestrially within the given cell. For example, assume a seven-cellfrequency reuse pattern including satellite radiotelephone cells 1-7. Incell 1, assume a set of uplink frequencies F1 is used. The uplinkfrequencies F2-F7 that are used in cells 2-7 also may be reusedterrestrially, without interference or with substantially lowinterference, within the cell 1. In these embodiments, the set offrequencies F2-F7 is monitored in cell 1 by the space-based component1630, to detect the radiation at frequencies F2-F7.

In the second embodiments of monitoring (Block 1420), frequencies thatare used for space-based communication within a given cell also are usedfor communication with the ancillary terrestrial network in the givencell, and interference may be reduced or canceled using an interferencereducer, as was described in connection with FIG. 1. Thus, in theseembodiments, a measure of the amount of interference that is reduced bythe interference reducer of FIG. 1 also can provide an indication of theamount of power that is being radiated by the ancillary terrestrialnetwork and/or the radiotelephones that communicate therewith in thegiven cell.

It will be understood that only the first embodiments of monitoring(Block 1410) may be used in some embodiments of the present invention toprovide a relatively straightforward technique for monitoring radiationby the ancillary terrestrial network and/or the radiotelephones thatcommunicate therewith, by monitoring radiation at frequencies that arenot used for space-based communications within the given satellite cell.Monitoring of the satellite band frequencies that are used by a givensatellite cell and that also are reused terrestrially within the samesatellite cell may not need to be performed. Instead, the amount ofradiation at those satellite cell frequencies that are also reusedterrestrially (intra-satellite beam wise) may be estimated orextrapolated based on the monitoring of the frequencies from other cellsthat are reused terrestrially in the given satellite cell. An input toderiving the estimate may be the ancillary terrestrial network loadingor traffic profile over the set of frequencies used in that satellitecell. In other embodiments, only the second embodiments of monitoring(Block 1420) may be used, by deriving a measure of the amount ofradiation that reaches the space-based component from the amount ofinterference that is reduced or canceled by the interference reducer. Instill other embodiments, both embodiments of monitoring (Blocks 1410 and1420) may be used.

Many techniques may be used to monitor frequencies from other satellitecells that are reused terrestrially in a given satellite cell (Block1410 of FIG. 14). In particular, the actual signals that are received atthe space-based component 1630 may be relayed to a gateway 1670 or othercomponent of the cellular satellite system by the space-based component.Alternatively, power level measurements may be obtained by thespace-based component 1630, so that only power level measurements mayneed to be relayed to the terrestrial components. Similarly, whenmonitoring frequencies from a given satellite cell that are reusedterrestrially in the given satellite cell (Block 1420 of FIG. 14), theinterfering signal may be provided to a gateway 1670, or the power ofthe signal that is being suppressed by the interference reducer may beused as a measurement of the amount of radiation by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith. Other techniques for measuring the power or signal level thatis radiated by the ancillary terrestrial network and/or theradiotelephones that communication therewith in a cell also may be used.

One technique for estimating (in the presence of noise) the aggregatesignal level generated by the ancillary terrestrial network and reachingthe space-based component, according to some embodiments of the presentinvention, now will be described. This technique can identify signalsfrom the ancillary terrestrial network and/or the plurality of secondradiotelephones that are received on the uplink in the presence ofnoise. In particular, in some embodiments, the received signal plusnoise power spectral density of the signals that are received on theuplink is measured at a plurality of frequencies in the satelliteradiotelephone frequency band. A difference is obtained between selectedones of the plurality of frequencies in the satellite radiotelephonefrequency band. This difference is used to reduce the effect of thenoise on the measurement.

More specifically, embodiments of the present invention that canestimate the aggregate signal level generated by the ancillaryterrestrial network and reaching the space-based component may bereferred to herein as “Delta-Power Spectral Density” (Δ-PSD)embodiments. The Δ-PSD embodiments derive their estimate of theinterference caused by the ancillary terrestrial network by performingmeasurements on the aggregate ancillary-signal-plus-noise over thesatellite uplink path. The Δ-PSD embodiments also can rely on knowledgeof frequency-domain signatures (i.e., the power spectral densitycharacteristic) of the signals that the ancillary terrestrial network isemitting. As an illustrative example, FIG. 17 shows the power spectraldensity of a GSM/GMSK carrier.

Some of the Δ-PSD embodiments measure the received signal plus thermalnoise power spectral density at the ancillary signal carrier centerfrequency and at frequencies corresponding to a given frequency offsetabove and below the carrier center frequency. Referring again to FIG.17, let P_(C)(dBm/Hz) be the measured signal plus noise density at the(GMSK) carrier center frequency F_(C) over the satellite return oruplink path. Let P_(HI) and P_(LOW) (dBm/Hz) denote the signal plusnoise densities measured at a given frequency offset F_(O) above andbelow the center frequency F_(C), respectively. Finally, let P_(O) bethe arithmetic average of P_(HI) and P_(LOW) (as defined in FIG. 17). Inthe absence of noise, the difference between P_(C) and P_(O), indicatedas Δ in FIG. 17, is the known difference in (GMSK) power spectraldensity for the given frequency offset F_(O).

Let C (dBm) be the aggregate ancillary signal power received over thesatellite return path for a given channel and spot beam (where the spotbeam does not use the same channel for satellite communications). Then,C can be estimated from the measurements P_(C) and P_(O) (in thepresence of noise) using the following equations:

C=10 log(10^(P) ^(C) ^(/10)−10^(P) ^(O) ^(/10))−K ₁ +K ₂,

K ₁=10 log (1−10^(−Δ/10)),

Δ=P _(C) −P _(O)

The quantity Δ is in dB, and, as FIG. 17 illustrates, denotes thedifference between P_(C) and P_(O) as measured (or calculated) in anoiseless environment. The quantity K₂ is a constant that relates thetotal carrier power C to the corresponding power spectral density at thecarrier center frequency. For GSM/GMSK, K₂ was measured to be about 51.0dB-Hz. That is, for a carrier power spectral density (at the center ofthe carrier's spectrum) of X dBm/Hz, the corresponding total carrierpower is X+51 dBm.

Accordingly, the quantity C may be used to estimate the aggregateancillary signal power without the need to explicitly measure theoverlaid channel thermal noise density. This can reduce or eliminate thepotential network disruption of having to remove the ancillary carriersin order to obtain a calibrated noise-only measurement.

In some embodiments of the Δ-PSD technique, the measured power spectraldensities P_(C) and P_(O) generally will exhibit time fluctuations thatmay be averaged out before the power spectral densities are used in theabove equation. It also may be desirable to apply sufficient timeaveraging on the measurements P_(C) and P_(O) to reduce the variationsto the order of about ±0.1 dB in some embodiments. In order to reduceany effects of level changes that may occur during the averaging period,it may also be desirable to perform the P_(C) and P_(O) measurements atthe same time.

Moreover, for the above equation to yield accurate results, thetime-averaged thermal noise density in the satellite channel may need tobe essentially flat over the measurement span of F_(C)±F_(O). However, astable passband variation (such as due to filtering) can be accommodatedby applying appropriate correction factors to the P_(C) and P_(O)measured values.

In some embodiments, the selection of the measurement frequency offsetF_(O) may be driven by two competing factors. First, a larger value forF_(O) increases the Δ value shown in FIG. 17, which in turn can improvethe accuracy and repeatability of the equation results. However, as alsoshown in FIG. 17, the GSM/GMSK spectrum produces significant energyspillover into the adjacent channels. Therefore, when measuring P_(O), asmaller value for F_(O) may provide greater discrimination againstsignal energy from the adjacent channel.

Finally, if in an adjacent satellite spot beam a radiotelephone insatellite mode is transmitting co-frequency with the ancillaryterrestrial network, the power received in the spot beam performing theancillary signal measurements, due to the radiotelephone transmitting insatellite mode in the adjacent beam, may be larger than the aggregateancillary signal level that is being measured. Since the measurement maynot discriminate between satellite-mode and ancillary-mode signal power,adjacent-beam satellite transmissions may need to be suspended aroundthe center frequency F_(C) and F_(O) offsets during the P_(C) and P_(O)measurements.

Referring again to FIG. 13, at Block 1320, a determination is made as towhether excessive signals are radiated by the ancillary terrestrialnetwork. Excessive radiation may be measured on all or some frequencies,in all or some geographic areas, and/or at a point in time or over anextended period of time. Many techniques for dynamically or staticallymeasuring whether excessive signals are being radiated by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith will be understood by those having skill in the art and neednot be described further herein.

Still referring to FIG. 13, at Blocks 1330 and 1340, the ancillaryterrestrial network radiation is reduced, or increased or allowed toremain the same, respectively, based on the signal measurement. It willbe understood that the increase or decrease (or no action taken) inancillary terrestrial network and/or radiotelephone radiation may beaccomplished across the entire ancillary terrestrial network and/orradiotelephones, or over only selective ancillary terrestrial componentsand/or radiotelephones in the ancillary terrestrial network. Moreover,increases or decreases (or no action taken) may be performed selectivelyat various frequencies or at all frequencies in the uplink frequencyband.

In some embodiments of the present invention, the satelliteradiotelephone system has knowledge, at any given time, of the positionof each active radiotelephone, whether in the satellite mode or in theancillary terrestrial mode. For example, the radiotelephone may beequipped with GPS-based position determination systems. Each activeradiotelephone can periodically report to the system a plurality ofparameters including its position coordinates, its output power level,and whether or not it is capable of receiving and decoding the satelliteBroadcast Control CHannel (BCCH).

In response to the monitoring of the aggregate ancillary terrestrialsignal reaching the space-based component, certain radiotelephones thatare active in the ancillary terrestrial mode and are capable ofreceiving the satellite BCCH, may be commanded to switch over to thesatellite mode. This switch may occur if the level of the aggregateancillary signal, as monitored by the space-based component, is eitherapproaching, has reached, or has exceeded a predetermined powerthreshold. The radiotelephones that are able to receive and decode thesatellite BCCH and are radiating at or near maximum power can becandidates for handing off to the space-based component.

In still other embodiments, the potential interference may be reduced oreliminated by selecting a vocoder rate of a radiotelephone interrestrial mode in response to the aggregate interference levelprovided by monitoring and the radiotelephone's output power. Inparticular, the radiotelephone may contain at least two groups ofvocoders. A vocoder from the first group of vocoders may be selected andused when the radiotelephone is engaged in satellite-mode voicecommunications. The first group of vocoders may include, for example, a3.6 kbps vocoder, a 2.4 kbps vocoder, and a 2.0 kbps vocoder. A vocoderfrom the second group of vocoders may be selected and used when theradiotelephone is engaged in ancillary terrestrial mode voicecommunications. The second vocoder group may include, for example, afull-rate GSM vocoder, a half-rate GSM vocoder, a quarter-rate GSMvocoder, a 3.6 kbps vocoder, a 2.4 kbps vocoder, and a 2.0 kbps vocoder.

In general, as the vocoder rate is reduced, fewer information bits aregenerated and thus fewer bits may need to be transmitted per unit oftime. Therefore, keeping the transmitted energy per bit invariant (sincethe energy per bit generally dictates communications performance), atransmitting device such as a radiotelephone can reduce its averageoutput power level by using a lower rate vocoder.

When monitoring of the aggregate signal power that is generated byancillary terrestrial operations according to embodiments of theinvention reveals a level of interference that is undesirable orunacceptable, action can be taken to reduce the interference. Thisaction may entail sending a command to the radiotelephones that areoperating at or near maximum power to reduce their vocoder rate. If needbe, other radiotelephones that are not operating at or near maximumpower may also be commanded to reduce their vocoder rates to relieve theinterference situation further.

Additional qualitative considerations for systems and methods formonitoring terrestrially reused satellite frequencies to reduceinterference according to some embodiments of the present invention nowwill be described. In particular, referring again to FIG. 16, in orderto allow the network components (space and ancillary terrestrial) tocontinue, over the life of the system, to interoperate with high ormaximum efficiency, embodiments of the invention can include built-inmonitoring. The space-based segment can monitor, in real time, theaggregate ancillary signal that is generated by ancillary terrestrialoperations. Based on inputs from monitoring, closed loop feedbackcontrol may be imposed on some or all of ancillary terrestrialcomponents in the ancillary terrestrial network 1610, such that theaggregate ancillary signal being measured by the space-based component1630 does not exceed potentially harmful limits. The space-basedcomponent 1630 associated with the system containing and operating theancillary terrestrial network generally will be more susceptible to theeffects of the aggregate ancillary signal because the elevation anglesto the space-based component 1630 generally will be greater than thecorresponding elevation angles of other satellites 1650. For example,the average elevation angle (over the continental United States) toMSV's 101° W satellite is 43°. The same average, taken for the Inmarsat3 satellite at 54° W is 30°. Moreover, the satellite antennadiscrimination relative to terrestrial reuse of frequencies of thesystem containing and operating the ancillary terrestrial network willgenerally be less of other satellites 1650.

Accordingly, other cellular satellite systems such as Inmarsat can beprotected because potentially harmful ancillary signal levels 1620 willbe seen first by the space-based component 1630 and thus can bemaintained under control. The aggregate signal power being received atthe space-based component 1630 from its ancillary terrestrial componentsand/or radiotelephones that operate in the ancillary terrestrial network1610 may be monitored (Block 1310 of FIG. 13), and may be limitedaccordingly to the extent necessary or desirable to protect satellite1630 operations and those of other satellite radiotelephone systems1650.

Several levels of monitoring of the aggregate signal level generated byancillary terrestrial frequency reuse in the satellite radiotelephonesystem may be performed by the space-based component 1630, according tosome embodiments of the invention, In some embodiments, every returnlink beam formed by the space-based component 1630 can monitor theaggregate signal level generated by that component of the overallancillary terrestrial network 1610 that exists within the geographicarea spanned by the relevant satellite beam, i.e., intra-system,intra-beam monitoring. By combining (summing) the contributions from theplurality of satellite beams, the total aggregate signal generated bythe entire ancillary network and reaching the space-based component 1630can be measured and recorded. A centralized system controller 1680 canmonitor signal levels and, via closed-loop feedback control, can setappropriate limits on ancillary traffic. This is further explained asfollows:

Let S_(n)(t,f) denote the aggregate ancillary signal power, at carrierfrequency f, that is generated within the service area of the n^(th)satellite beam, at time t, and reaching the space-based component 1630.This signal power may be measured and recorded by the system at regularintervals of time, {t, t+Δτ, t+2Δτ, . . . }, and this can be performedfor each beam (n=1, 2, . . . , N) and for each co-channel ancillarycarrier frequency f. Based on this information, the total aggregateancillary signal power reaching a distant satellite 1650 at time t, andat co-channel carrier frequency f can be evaluated as follows:

S _(T)(t,f)=α₁ξ₁S₁(t,f)+α₂ξ₂S₂(t,f)+ . . . +α_(N)ξ_(N)S_(N)(t,f),

where,α_(n)≡antenna discrimination of the distant satellite 1650 relative togeographic area spanned by the n^(th) satellite beam of the space-basedcomponent 1630, (n=1, 2, . . . , N),S_(n)(t,f)≡aggregate ancillary signal power received by the n^(th) beamof space-based component 1630 at time t, and at co-channel carrierfrequency f,and,ξ_(n)≡elevation-dependent statistical adjustment factor.

If, relative to the area spanned by the n^(th) beam of the space-basedcomponent 1630, the elevation angle of the distant satellite 1650 islower than that of the space-based component 1630, then, for that beam(for that value of n), the elevation-dependent statistical adjustmentfactor value may be set to unity. This can provide extra protection forthe distant satellite system by upper-bounding (in the above equation)the aggregate ancillary signal power that can reach the distantsatellite (since as the elevation angle decreases, the probability ofblockage increases). In the generally unlikely event that, relative tothe area spanned by the n^(th) beam of the space-based component 1630,the elevation angle of the distant satellite 1650 is higher than that ofthe space-based component 1630, the value of the correspondingelevation-dependent statistical adjustment factor can be setdifferently. In this case, it can be set to a value that is greater thanunity, by an appropriate amount, to account for the effect (since as theelevation angle increases, the probability of blockage decreases).Statistically, the average level of shielding (average signalattenuation) to a geostationary satellite can be expressed by a linearregression fit of the mean attenuation as a function of the elevationangle. The specific relationship:

Mean Attenuation (dB)=19.2−(0.28)(Elevation°),

can be used to predict the level of signal attenuation and, therefore,the aggregate signal to be received by a geostationary satellite.

FIG. 15 is a block diagram of embodiments of monitoring frequencies fromother satellite cells that are reused terrestrially in a given satellitecell (Block 1410 of FIG. 14) that may be practiced by a space-basedcomponent 1630 of FIG. 16. In particular, antenna elements 1-N of thespace-based component 1630 are connected to a beam-forming network 1510,that produces a plurality of beam signals S₁(t) . . . S_(M)(t). Thesesignals are provided to channelizers 1520, which produce a plurality ofsatellite communication channels 1530 that are provided to a FrequencyDivision Multiplexing (FDM) feeder link processor 1540. The feeder linkprocessor output is provided to the feeder link electronics, to providethe signal for the satellite return feeder link. A controller 1550controls the beam forming network 1510, the channelizers 1520 and thefeeder link processor 1540.

Still referring to FIG. 15, according to some embodiments of theinvention, a selector 1560 can select outputs 1530′ of the channelizers1520 and provide these outputs to the feeder link processor 1540. Thus,the frequencies from other satellite cells that are reused terrestriallyin a given satellite cell may be sent to the feeder link by the selector1560. It will be understood that not all ancillary signals of all beamsneed to be sent to the ground simultaneously. Moreover, in someembodiments, ancillary signals of beams need not be sent to the ground.Rather, power measurements may be taken on board the space-basedcomponent 1630 and only those measurements may be sent to the ground viathe satellite TT&C link.

Still other embodiments of monitoring signals on the satelliteradiotelephone return link (Block 1310 of FIG. 13) may use a modelingtechnique to monitor the physical signals. In particular, it will beunderstood that the system 100 of FIG. 1 generally has knowledge of thelocations of each ancillary terrestrial component 140 and eachradiotelephone 120. Knowledge of the locations of the radiotelephones120 may be obtained by a built-in GPS system and/or by the exchange ofcommunication signals during radiotelephone communications. For eachgeographical area that is covered by a space-based component 110, amodel may be built that includes geographic features, buildings, roadsand/or other information regarding the morphology that may attenuate orblock radiation by the radiotelephones and/or the ancillary terrestrialnetwork. Then, a computer simulation may be used to simulate the levelof interference to the space-based component 110 and/or satellite 1650based on this model.

In particular, still referring to FIG. 1, in the Ancillary TerrestrialNetwork (ATN), users actively engaged in calls may at times also haveclear Line-Of-Sight (LOS) to the space-based component 110, or tosatellites of other service providers (referred to herein as “adjacent”satellites). Where clear LOS exists to an adjacent satellite, thoseusers' transmissions can contribute to increasing the noise floor ΔT/Tin the co-frequency channel of the adjacent satellite. Thus, it may bedesired for cellular satellite radiotelephone systems according to someembodiments of the invention to maintain the total co-frequencyinterference due to ATN users to within some established ΔT/T allowance.Satellite radiotelephone systems and methods according to someembodiments of the invention may not be able to monitor the adjacentsatellite noise floor directly, so the interference contribution fromthe ATN may be estimated from known system parameters and probabilities.Therefore, it may be desirable to have the capability to accuratelydetermine whether each active ATN user has clear LOS to the adjacentsatellite, to allow an estimate of the total ATN interference, andthereby allow that the ΔT/T allowance to not be exceeded.

To this end, according to some embodiments of the invention, thegeo-location of the radiotelephones can be used to determine whether anactive ATN user has simultaneous LOS to an adjacent satellite. Tofacilitate these embodiments, each radiotelephone may be equipped withan integrated geo-location capability, such as a GPS receiver. During acall, the user's position information can be continually or periodicallytransmitted to a Network Control Center (NCC) as part of normal in-callsignaling. For each city where an ATN is deployed, the NCC can maintaina detailed geographical database map of the area served, includingbuilding heights and/or other structural dimensions. Such databases arealready in use supporting activities such as planning cellular basestation locations. The NCC can simultaneously track the locations ofeach active ATN user within its “virtual city” database. By knowing theuser's reported position, the relative positions of buildings in thedatabase, and the look angles to satellites of interest, the existenceof clear LOS to any given satellite can be calculated.

The accuracy of the LOS calculation described above may depend, at leastin part, on the quality of the user's position fix. GPS accuracygenerally is affected by the number of GPS satellites in view. Inrelatively open areas, this accuracy may be to within a few meters orbetter, but may degrade in urban areas, where the ATN generally will bedeployed due to satellite blockages in “urban canyons”. Therefore, inaddition to reporting its position, the radiotelephones may also reportmetrics conveying the quality of the fix, such as the number of GPSsatellites in view. The NCC can translate the reported quality-of-fixinformation into a corresponding position tolerance, defining a radiusof uncertainty around the reported position. Thus, the higher thequality of fix, the smaller this radius of uncertainty. By solving theLOS calculation at all locations within this radius of uncertainty andintegrating the results, an overall probability of LOS can be assigned,and the estimated interference contribution can be weighted by thisprobability. If the radiotelephone cannot provide a fix and reports nosatellites in view, this may indicate that the user is completelyshielded from the outside, such as being inside a building, and the NCCmay assign a very low LOS probability in this case. If a fix cannot beprovided but one or two satellites are in view, the NCC can assign anappropriately higher LOS probability based on statistical averages.

According to still other embodiments, a GPS augmentation system (similarto Snaptrack) may be used to assist GPS in dense urban areas. Such asystem, if integrated into the ATN architecture, could potentiallyenable position reporting even inside buildings, thereby increasingposition reporting accuracy.

Given potentially thousands of ATN users at any time, the sum of theinterference contributions from each user, derived using thegeo-location described above, can provide an accurate estimate of totalco-frequency interference from the ATN into adjacent satellites. If itis desired or necessary to terminate or reassign calls to reduce theinterference, the most likely candidates may be those users transmittingat the highest assigned powers with the highest calculated LOSprobability.

Finally, according to still other embodiments, a space-based componentmay be co-located with a satellite of another system. This co-locatedspace-based component can provide a direct way to measure and monitorthe power level of the aggregate ancillary signal reaching the satelliteof the other system.

Accordingly, some embodiments of the invention can provide a space-basedcomponent that is configured to receive wireless communications fromradiotelephones in a satellite footprint over one or more frequencies ina satellite radiotelephone frequency band. An ancillary terrestrialnetwork is configured to receive wireless communications fromradiotelephones in the satellite footprint, using frequencies other thanthe one or more frequencies that are used in a given satellite celland/or using the same one or more frequencies that are used in the givensatellite cell. The space-based component receives at least some of thewireless communications between the radiotelephones and the ancillaryterrestrial network as interference. The signals that are received bythe space-based component as interference are monitored. If excessivesignals are present, the radiation by the radiotelephones and/or theancillary terrestrial network can be reduced. If excessive signals arenot present, the radiation can be increased if so desired, or allowed toremain unchanged. Interference with other satellite systems by theancillary terrestrial network and/or the radiotelephones thatcommunicate therewith thereby may be reduced or prevented.

Additional Embodiments of Monitoring Terrestrially Reused SatelliteFrequencies to Reduce Potential Interference

The previous section described many embodiments of systems and methodsfor monitoring terrestrially reused satellite frequencies that cancontrol the number, geographic distribution and/or power of theradiation by the ancillary terrestrial network and/or theradiotelephones that communicate therewith, to reduce or eliminatepotential interference with other satellite radiotelephone systems.Interference within the given satellite radiotelephone system(intra-system interference) also may be reduced by this monitoring,according to some embodiments of the present invention, Additionalembodiments of monitoring terrestrially reused satellite frequencies toreduce potential interference now will be described. These embodimentsmay provide additional embodiments of a monitoring operation, forexample as illustrated in Block 1310 of FIG. 13.

In general, some embodiments of the present invention provide aspace-based component such as the space-based component 110 of FIG. 1that is configured to wirelessly communicate with radiotelephones, suchas the plurality of first radiotelephones 120 a of FIG. 1, in asatellite footprint over a satellite radiotelephone frequency band. Thesatellite footprint is divided into a plurality of satellite cells, forexample satellite cells 130-130″″ of FIG. 1, in which subsets of thesatellite radiotelephone frequency band are spatially reused in aspatial reuse pattern. An ancillary terrestrial network that includes atleast one ancillary terrestrial component, such as the ancillaryterrestrial component 140 of FIG. 1, is configured to wirelesslycommunicate with radiotelephones, such as the plurality of secondradiotelephones 120 b of FIG. 1 in the satellite footprint over at leastsome of the satellite radiotelephone frequency band, to therebyterrestrially reuse the at least some of the satellite radiotelephonefrequency band. It will be understood that the functions of the firstand second radiotelephones, to communicate with the space-basedcomponent and the ancillary terrestrial component, may be performed in asingle radiotelephone at various points in time. Moreover, at least someof the radiotelephones may simultaneously communicate with thespace-based component, for example to receive communications, and withthe ancillary terrestrial network, for example to transmitcommunications.

A monitor, which can be part of a gateway 160 of FIG. 1 and/or 1670 ofFIG. 16, part of a controller 1680 of FIG. 16, part of any othercomponent of the satellite radiotelephone system and/or a discreteentity, is configured to monitor wireless radiation at the space-basedcomponent by the ancillary terrestrial network and/or theradiotelephones in satellite cells that adjoin a predetermined cell,such as the at least one of satellite cells 130′-130″″ that adjoinsatellite cell 130 and/or in the satellite cell 130 itself, in at leastpart of the subset of the satellite radiotelephone frequency band thatis assigned to the predetermined satellite cell 130 for space-basedcomponent communications. A controller, which can be part of the gateway160, 1670, a separate controller 1680, part of any other component ofthe satellite radiotelephone system, and/or a discrete entity, isconfigured to adjust the radiation by the ancillary terrestrial networkand/or the radiotelephones in response to the monitor.

Some embodiments of the present invention now will be described inconnection with FIG. 18. Referring now to FIG. 18, a seven-cellfrequency reuse pattern including satellite radiotelephone cells 1-7 isillustrated. In a predetermined satellite cell, such as cell 1, asindicated by the cross-hatched regions of FIG. 18, assume a set ofsatellite frequencies F1 is assigned. The sets of satellite frequenciesF2-F7 that are assigned to satellite cells 2-7 that adjoin thepredetermined satellite cell 1, also may be assigned terrestrially,without interference or with substantially low interference, within cell1. Moreover, as also shown by the hatched area of FIG. 18, the set offrequencies F1 may be reused terrestrially outside satellite cells 1,and separated by satellite cells 1 by a spatial guardband shown by theunshaded rings surrounding the satellite cells 1. The use of spatialguardbands is described in copending application Ser. No. 10/180,281,filed Jun. 26, 2002, entitled Spatial Guardbands for Terrestrial Reuseof Satellite Frequencies to co-inventor Karabinis, and assigned to theassignee of the present application, the disclosure of which is herebyincorporated herein by reference in its entirety as if set forth fullyherein. Accordingly, the provision of spatial guardbands need not bedescribed in further detail herein. Moreover, in other embodiments,spatial guardbands need not be used.

Continuing with the description of FIG. 18, three representative ATCsare shown, labeled A, B and C. Since ATC A is located in an area ofoverlap between satellite cells 2, 4 and 6, ATC A can terrestriallyreuse frequencies from satellite frequency sets F1, F3, F5 and F7,according to some embodiments of the present invention. ATC B is locatedwithin satellite cell 2, and in close proximity to satellite cells 5 and7, so that ATC B can terrestrially reuse frequencies from satellitefrequency sets F1, F3, F4 and F6, according to some embodiments of thepresent invention. Finally, ATC C is in satellite cell 7 and in closeproximity to satellite cells 3 and 4. Accordingly, ATC C canterrestrially reuse frequencies from satellite frequency sets F1, F2, F5and F6, with reduced or no interference with the space-based use ofthese frequencies. The satellite uplink carrier frame may be arranged asa Time Division Multiple Access (TDMA) frame, such as was described, forexample, in FIG. 11, with, for example, eight slots.

As was previously described, monitoring may be performed intra-beam, toreduce or avoid beam discrimination losses. As shown in FIG. 18, thesatellite radiotelephone cells that adjoin a given satelliteradiotelephone cell, also referred to as “vicinity beams” or “vicinitycells”, may be used to monitor the set of frequencies that are used inthe given satellite cell, to identify ATC and/or radiotelephoneemissions that reach the space-based component. The vicinity beams of asatellite cell 1 are outlined in bold in FIG. 18, and may lie betweenthe related spatial guardband (if any) and the outer boundary ofsatellite cells 2-7. Thus, for example, the uplink beams of satellitecells 2-7 may be used to monitor the power levels of at least somefrequencies in set F1 that are generated by the ATCs and/orradiotelephones in satellite radiotelephone cells 2-7. The detectedpower levels of uplink frequencies in set F1 over these vicinity beamsthen may be summed in order to determine the vicinity aggregate noiseand interference power. As was already described in FIG. 13, based onthis monitoring, the radiation by the ancillary terrestrial networkand/or radiotelephones may be increased, reduced or remain the same.

It will be understood that FIG. 18 and the present descriptionillustrates satellite cell 1 as a central cell and satellite cells 2-7as vicinity cells. However, similar operations may be performed withrespect to remaining cells 2-7 as central cells, using their assignedfrequency sets F2-F7. These similar operations are not shown in FIG. 18,or described in the present description, for the sake of clarity.

In other embodiments of the present invention, wireless radiation at thespace-based component, by the ancillary terrestrial network and/or theradiotelephones in satellite cells that are outside a predeterminedsatellite cell may be performed. In these embodiments, monitoring takesplace not only of radiation from the satellite cells that adjoin thepredetermined cell, but also of satellite cells that are a greaterdistance from the predetermined satellite cell.

It may be desirable to obtain an accurate indication of theterrestrially reused radiation that is generated by the ancillaryterrestrial network and/or the radiotelephones that communicatetherewith, so that power levels of the ancillary terrestrial networkand/or the radiotelephones need not be reduced unnecessarily.Accordingly, it may be desirable to obtain the aggregate noise andinterference power of the ancillary terrestrial network and/or theradiotelephones outside satellite radiotelephone cells 1 at one or moresatellite uplink frequencies belonging to set F1, without including thecontribution of the satellite uplink frequencies of F1 that are used insatellite cells 1 themselves for satellite communications. Stateddifferently, when satellite radiotelephone cells 2-7 monitor a reuseduplink frequency of F1 that is transmitted by the ancillary terrestrialnetwork and/or radiotelephones during terrestrial communications, it maybe desirable to exclude from this monitoring the radiation of thatuplink frequency of F1 that is used by satellite cells 1 themselves forsatellite uplink communications.

Accordingly, in some embodiments of the invention, the vicinityaggregate measurement on a frequency of F1 is taken when that satelliteuplink communications frequency of F1 is silent over at least one timeslot within satellite radiotelephone cell 1 that is encircled by thevicinity. By taking the vicinity aggregate power measurement of a givenfrequency outside a given satellite cell while the given satellite cellis silent on the given frequency, a more accurate estimation of thepotential interference by ATC and/or radiotelephone reuse of thatsatellite uplink frequency may be obtained. Stated differently,monitoring may be performed at a time that the at least part of thesubset of the satellite radiotelephone frequency band that is assignedto the predetermined satellite cell for space-based componentscommunications is not actually being used in the predetermined satellitecell for space-based component communications.

Many embodiments for silencing satellite radiotelephone communicationsin a given set of uplink frequencies may be provided according toembodiments of the present invention. In some embodiments, the satelliteradiotelephone system may know when these times are occurring, as aresult of voice or data inactivity. Stated differently, monitoring takesplace at a time that the at least part of the subset of the satelliteradiotelephone frequency band that is assigned to the predeterminedsatellite cell for space-based component communications is not actuallybeing used in the predetermined satellite cell for space-based componentcommunications due to inactivity of at least one radiotelephone in thepredetermined satellite cell. In other embodiments, the system can forcethese non-activity times to occur, for example via Fast AssociatedControl CHannel (FACCH) signaling, so as to allow the monitoring to takeplace. In other words, the monitor may include a silencer that isconfigured to silence the at least part of the satellite radiotelephonefrequency band that is assigned to the predetermined satellite cell forspace-based component communications. In these embodiments, monitoringmay take place at a time that the at least part of the subset of thesatellite radiotelephone frequency band that is assigned to thepredetermined satellite cell for space-based component communications issilenced by the silencer.

In still other embodiments, it may be desirable to obtain a measurementof the thermal noise floor in which the system is operating, for examplethe thermal noise floor in the predetermined satellite cell and/or inthe satellite cells that adjoin the predetermined satellite cell, toobtain a more accurate measurement of the potentially interferingterrestrially reused frequencies. In order to calibrate the thermalnoise floor, other embodiments of the invention may use a silencer tosynchronize all vicinity ATCs that reuse an uplink frequency of F1 andperiodically command all transmissions to cease at that frequency for apredetermined time interval or intervals.

Thus, in some embodiments, a thermal noise floor in the satellite cellsthat adjoin the predetermined satellite cell is determined at a timethat the ancillary terrestrial network that is in the satellite cellsthat adjoin the predetermined satellite cell is not communicating withthe radiotelephones using the at least part of the subset of thesatellite radiotelephone frequency band that is assigned to thepredetermined satellite cell for space-based component communications.In still other embodiments, this synchronized cessation of terrestrialreuse of satellite uplink frequencies of F1 may be coordinated with thenon-activity of uplink frequencies of F1 within a vicinity's satelliteradiotelephone cell I and/or within other satellite cells using thesatellite uplink frequencies of F1 for satellite communications.

Thus, in other embodiments, the thermal noise floor is determined at atime that the ancillary terrestrial components and/or theradiotelephones that are in the satellite cells that adjoin thepredetermined satellite cell are not communicating using the at leastpart of the subset of the satellite radiotelephone frequency band thatis assigned to the predetermined satellite cell for space-basedcomponent communications, and the radiotelephones in the predeterminedsatellite cell also are not communicating with the space-based componentusing the at least part of the subset of the satellite radiotelephonefrequency band that is assigned to the predetermined cell forspace-based component communications.

It will be understood by those having skill in the art that theabove-described embodiments that silence the satellite uplinkfrequencies of F1 and/or the terrestrial reuse of the satellite uplinkfrequencies of F1 for a limited period of time, need not preclude theability to relay voice and/or data information. For example, in voicemode, the use of a quarter rate GSM vocoder can allow theradiotelephones to transmit once every four TDMA frames, while remainingsilent over three frames. Similar principles can be applied to datatransmission, with or without some potential sacrifice of datathroughput.

In still other embodiments of the present invention, an averagesatellite antenna pattern discrimination may be used to convert themeasured aggregate vicinity ATC interference at a given satellite uplinkfrequency of F1, to an equivalent thermal noise level increase on thegiven satellite uplink frequency of F1 for satellite communications.Average antenna discrimination may be obtained by evaluating the antennadiscrimination of satellite cell 1 relative to each ATC that is in thevicinity of the satellite cell 1, and is reusing the given satelliteuplink frequency of F1, for example by measuring the BCCH of therelevant satellite cell 1 (BCCH 1) at each ATC. In this regard, it willbe understood that BCCH 1 bursts corresponding to neighboring cells 1may be staggered in time to reduce, avoid or minimize interference. Theaverage antenna discrimination then may be obtained by:

${{{Average}\mspace{14mu} {antenna}\mspace{14mu} {discrimination}} = \frac{{\alpha_{A}P_{A}} + {\alpha_{B}P_{B}} + {\alpha_{C}P_{C}}}{P_{A} + P_{B} + P_{C}}};$

-   -   where α is the antenna beam discrimination of the relevant        vicinity cell 1 at a given ATC of that vicinity, of a specified        satellite cell using the given frequency of F1 for ATC        communications; and    -   where P is the power due to the given ATC users on the given        satellite uplink frequency of F1, detected by the vicinity        satellite cell that contains the ATC.

The subscripts A, B and C relate to the ATC that the quantity a or P isassociated with. FIG. 18, for example, illustrates 3 ATCs labeled as A,B, C existing within the vicinity of a satellite cell 1.

If a vicinity cell (2-7) contains a plurality of ATCs that are reusing agiven frequency of F1, the minimum satellite cell 1 discrimination thatis detected, relative to one of the plurality of the ATCs, may be usedin the above equation to calculate the average antenna discrimination.This will yield a worst case (minimum) antenna discrimination for thevicinity. This average antenna discrimination may be used to convert themeasured aggregate vicinity ATC interference at a frequency of F1 to anequivalent thermal noise level increase on that frequency of F1 forsatellite communications.

Other embodiments of the present invention need not use intra-beammeasurements in vicinity satellite beams to monitor for potentialinterference. Rather, a measurement on a satellite uplink frequency ofF1 itself may be taken in a satellite radiotelephone cell 1 during ashort time period when satellite communications in the satellite cell 1are silenced. By measuring the power level in a satellite cell 1 of asatellite uplink frequency of F1 at a time when satellite communicationsusing the frequency of F1 are known to be silent, a measurement ofpotential interference due to terrestrial reuse of the satellitefrequency of F1 may be obtained.

Thus, in these embodiments, the monitor is configured to monitorwireless radiation at the space-based component from the predeterminedsatellite cell, in the at least part of the subset of the satelliteradiotelephone frequency band that is assigned to the predeterminedsatellite cell for space-based component communications, at a time thatthe at least part of the subset of the satellite radiotelephonefrequency band that is assigned to the predetermined satellite cell forspace-based component communications is not actually being used in thepredetermined satellite cell for space-based component communications.In these embodiments, calibration to the thermal noise floor may beprovided using any of the techniques that were described above, forexample by silencing the vicinity ATCs that use the frequency of F1.Noise floor calibration also may be made via mathematical analysis. Inother embodiments, noise floor calibration also may be performed byusing a relatively small sliver of spectrum over which neither ATCs norSBCs are transmitting.

Other alternate embodiments can reduce the effect of satellitecommunications using uplink frequencies of F1 on the accuracy ofmonitoring the effect of terrestrial reuse of satellite uplinkfrequencies of F1, without the need to silence the satellitecommunications in cell 1 that use uplink frequencies of F1. In theseembodiments, the monitor is configured to determine radiation by theradiotelephones in the predetermined satellite cell, of the at leastpart of the subset of the satellite radiotelephone frequency band thatis assigned to the predetermined satellite cell for space-basedcomponent communications, while reducing a contribution of the radiationby the radiotelephones in the predetermined satellite cell of the atleast part of the subset of the satellite radiotelephone frequency bandthat is assigned to the predetermined satellite cell for space-basedcomponent communications, to the wireless radiation at the space-basedcomponent that is monitored by the monitor.

In some of these embodiments, each radiotelephone that is using afrequency of F1 for space-based communications can report its positionto the system. Based on this position information and the known patternof a satellite cell performing intra-beam ATC monitoring on a frequencyof F1, the contribution of that satellite radiotelephone of cell 1 usinga frequency of F1 for satellite communications may be determined and atleast partially subtracted out, to obtain an accurate assessment ofpotential interference by terrestrial reuse of satellite frequencies ofF1.

Accordingly, the monitor may be further configured to determineradiation by the radiotelephones in the predetermined satellite cell, inthe at least part of the subset of the satellite radiotelephonefrequency band that is assigned to the predetermined satellite cell forspace-based component communications, based on a position of at leastone radiotelephone in the predetermined satellite cell. In order toachieve the above, it may be desirable to also obtain the power of thesatellite communication carrier of F1 as received by the servingsatellite cell. Thus, these embodiments of the present invention neednot silence the satellite communication use of satellite uplinkfrequencies of F1 satellite cell 1 in order to perform accuratemonitoring but, rather, can determine the contribution of the satellitecommunication of satellite uplink frequencies of F1 based on theposition of at least one radiotelephone that is using a frequency of F1for satellite uplink communications. The need to silence the space-basedcommunications for a short period thereby may be avoided, at thepotential expense of more complex calculations.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

1. A radiotelephone for a satellite radiotelephone system that includesa space-based component and an ancillary terrestrial component that areconfigured to receive wireless communications from radiotelephones, theradiotelephone comprising: an electronics system that is configured totransmit wireless communications to the ancillary terrestrial componentover a range of satellite band forward link frequencies, wherein aradiotelephone output is gated to cease transmissions periodically overa period of time.
 2. A radiotelephone according to claim 1 wherein theelectronics system is configured to transmit wireless communications tothe ancillary terrestrial component over a range of satellite bandforward link frequencies using a Code Division Multiple Access (CDMA)air interface.
 3. A radiotelephone according to claim 1 wherein theradiotelephone output is gated to cease transmissions periodically forabout 3 msec over at least every 6 msec.
 4. A radiotelephone accordingto claim 1 wherein the radiotelephone output is selectively gated tocease transmissions periodically over a period of time in order toreduce a level of interference when the electronics system is configuredto transmit wireless communications to the ancillary terrestrialcomponent at about 1550 MHz and below.
 5. A method of operating aradiotelephone in a satellite radiotelephone system that includes aspace-based component and an ancillary terrestrial component that areconfigured to receive wireless communications from radiotelephones, theradiotelephone operating method comprising: transmitting wirelesscommunications to the ancillary terrestrial component over a range ofsatellite band forward link frequencies in a gated manner that ceasestransmissions periodically over a period of time.
 6. A method accordingto claim 5 wherein the transmitting comprises transmitting wirelesscommunications to the ancillary terrestrial component over a range ofsatellite band forward link frequencies using a Code Division MultipleAccess (CDMA) air interface.
 7. A method according to claim 5 whereinthe gated manner ceases transmissions periodically for about 3 msec overat least every 6 msec.
 8. A method according to claim 5 whereintransmitting in a gated manner is selectively performed whentransmitting wireless communications to the ancillary terrestrialcomponent over a range of satellite band forward link frequencies atabout 1550 MHz and below.
 9. An ancillary terrestrial component for asatellite radiotelephone system comprising: a receiver that is that isconfigured to receive wireless communications from a plurality ofradiotelephones over a range of satellite band forward link frequencies;and an electronics system that is configured to synchronize theplurality of radiotelephones to simultaneously cease transmissionsperiodically over a period of time.
 10. An ancillary terrestrialcomponent according to claim 9 wherein the receiver is configured toreceive wireless communications from a plurality of radiotelephones overa range of satellite band forward link frequencies using a Code DivisionMultiple Access (CDMA) air interface.
 11. An ancillary terrestrialcomponent according to claim 9 wherein the electronics system isconfigured to synchronize the plurality of radiotelephones tosimultaneously cease transmissions periodically for about 3 msec over atleast every 6 msec.
 12. An ancillary terrestrial component according toclaim 9 wherein the electronics system is configured to selectivelysynchronize the plurality of radiotelephones to simultaneously ceasetransmissions periodically over a period of time in order to reduce alevel of interference when a respective radiotelephone is configured totransmit wireless communications to the ancillary terrestrial componentat about 1550 MHz and below.
 13. An ancillary terrestrial network for asatellite radiotelephone system comprising: a plurality of receivers, arespective one of which is configured to receive wireless communicationsfrom a plurality of radiotelephones over a range of satellite bandforward link frequencies; and an electronics system that is configuredto synchronize the plurality of radiotelephones that are communicatingwith the plurality of receivers to simultaneously cease transmissionsperiodically over a period of time.
 14. An ancillary terrestrial networkaccording to claim 13 wherein the plurality of receivers are configuredto receive wireless communications from a plurality of radiotelephonesover a range of satellite band forward link frequencies using a CodeDivision Multiple Access (CDMA) air interface.
 15. An ancillaryterrestrial network according to claim 13 wherein the electronics systemis configured to synchronize the plurality of radiotelephones that arecommunicating with the plurality of receivers to simultaneously ceasetransmissions periodically for about 3 msec over at least every 6 msec.16. An ancillary terrestrial network according to claim 13 wherein theelectronics system is configured to selectively synchronize theplurality of radiotelephones that are communicating with the pluralityof receivers to simultaneously cease transmissions periodically over aperiod of time in order to reduce a level of interference when arespective radiotelephone is configured to transmit wirelesscommunications to the ancillary terrestrial component at about 1550 MHzand below.
 17. A method of operating an ancillary terrestrial componentfor a satellite radiotelephone system comprising: receiving wirelesscommunications at the ancillary terrestrial component from a pluralityof radiotelephones over a range of satellite band forward linkfrequencies; and synchronizing the plurality of radiotelephones by theancillary terrestrial component to simultaneously cease transmissionsperiodically over a period of time.
 18. A method according to claim 17wherein receiving comprises receiving wireless communications at theancillary terrestrial component from a plurality of radiotelephones overa range of satellite band forward link frequencies using a Code DivisionMultiple Access (CDMA) air interface.
 19. A method according to claim 17wherein synchronizing comprises synchronizing the plurality ofradiotelephones by the ancillary terrestrial component to simultaneouslycease transmissions periodically for about 3 msec over at least every 6msec.
 20. A method according to claim 17 wherein synchronizing comprisesselectively synchronizing the plurality of radiotelephones tosimultaneously cease transmissions periodically over a period of time inorder to reduce a level of interference when a respective radiotelephoneis configured to transmit wireless communications to the ancillaryterrestrial component at about 1550 MHz and below.
 21. A method ofoperating an ancillary terrestrial network for a satelliteradiotelephone system comprising: receiving wireless communications froma plurality of radiotelephones at a plurality of ancillary terrestrialcomponents over a range of satellite band forward link frequencies; andsynchronizing the plurality of radiotelephones that are communicatingwith the plurality of ancillary terrestrial components to simultaneouslycease transmissions periodically over a period of time.
 22. A methodaccording to claim 21 wherein receiving comprises receiving wirelesscommunications at the ancillary terrestrial components from theplurality of radiotelephones over a range of satellite band forward linkfrequencies using a Code Division Multiple Access (CDMA) air interface.23. A method according to claim 21 wherein synchronizing comprisessynchronizing the plurality of radiotelephones by the plurality ofancillary terrestrial components to simultaneously cease transmissionsperiodically for about 3 msec over at least every 6 msec.
 24. A methodaccording to claim 21 wherein synchronizing comprises selectivelysynchronizing the plurality of radiotelephones to simultaneously ceasetransmissions periodically over a period of time in order to reduce alevel of interference when a respective radiotelephone is configured totransmit wireless communications to a respective ancillary terrestrialcomponent at about 1550 MHz and below.